Variable reversible rectification process



July 26, 1955 REVERS/BLE' REC7'lF/ER V. C. WILLIAMS VARIABLE REVERSIBLERECTIFICATION PROCESS Filed Oct. 26, 1953 United States Patent VARABLEREVERSIBLE RECTIFICATION PROCESS Virgil C; Williams, Kirkwood, Mo.,assiguor to Mississippi River Fuel Corporation, St. Louis, Mo., acorporation of Delaware Application October 26, 1953, Serial No. 388,145

Claims. (Cl. 62-175.5)

This invention relates to improvements in process and apparatus forrectifying gaseous mixtures having different boiling points for the4individual components and, in particular, is concerned withv processand apparatus for separating a low boiling constituent from higherboiling constituents in a reversible rectification process.

This invention is a continuation-impart of my application for Processand Apparatus for Separation of Gases, Serial No. 303,276, filed August8, 1952, wherein process and apparatus for the separation of gases by areversible rectification process is disclosed. The present inventioncomprises. improvements in process and apparatus for reversiblyrectifying a low boiling constituent from higher boiling, constituentsin a gaseous mixture by the use of less complicated equipment, and by avsystem wherein the heating fiuid supplied to the rectification columncan be varied. both as to the total amount of flow charged therein, andthe amount of heating iiuid which flows entirely therethrough, such thatpart may .be divided out.

By means of this invention a portion of the` raw feed itself can be usedas a heating means within the rectification column. In order to providefor the most effrcient utilization of heat, p'art of this feedintroduced into the rectification column can be divided from the mainstream within this column and removed therefrom. Thus, where the rawfeed in the column has been. cooled to the dew-point, most of thecooling effect of the downcoming liquid feed within the columnl which istol be rectified would ordinarily be utilized in latent heat ofcondensation in so cooling the portion of the feed used for heatingpurposes. To prevent this and. to obtain as low a temperature as ispossible, a portion is divided and recycled to the system for furthercooling prior to its introduction in the column with the remainder ofthe feed gas. The portion of the feed that is. used in the rectificationcolumn for heating purposes that has not been divided is caused to beled upwardly within the column in heat exchange relationship with thedescending feed fluid which is to be rectified, and is removed adjacentto the inlet of the feed to the column after being in heat exchangerelationship with the descending feed fluid throughout. The heatingfiuid which is.l so caused to be moved upwardly in this heat exchangerelationship after being removed from the column is then further cooledto a low temperature where it'. can be introduced with the remainder ofthe initial feed. to the column for rectification.

The only other source of refrigeration required in this process issupplied by the rectified gas having the lowest boiling point in thegaseous mixture which imparts a cooling effect derived from its own lowtemperature leaving the rectication column. A further cooling effect isestablished by an isentropic expansion within a turbo expander whichdoes additional work in an initial compression stage on the feed gaseousmixture introduced into this system.

This processl is adaptable for being used with gaseous 2,713,781Patented July 26, 1955 ,a ICC mixtures having various compositions wherethe constituents have varying boiling points without the necessity ofadding or abstracting heat from any outside means. This process is alsoparticularly well suited for they separation of methane from natural gasmixtures and will be so described in connection therewith, but it isv tobe understood that by means of this invention other gaseous mixtures canbe rectified according to the teachings herein with a small equipmentoutlay in a process which is well adapted for modification and extensionto other 4 feed and end product requirements.

It is, accordingly, an object of this invention to` provide process andapparatus for reversibly rectifying a gaseous mixture wherein theseparation. is effected by' a reversible rectification, and the heatsource therefor is supplied by the feed gas itself, and wherein part ofthis feed gas usedv for heating purposes may be taken from the columnprior to fullling the entire heating requirement.

It is a further object of this invention to provideA process andapparatus for reversibly rectifying a gaseous mixture wherein theheating requirements within the rectification column are supplied by aportion of the feed mixture itself, and in which a portion of this feedused for heating is divided from the remainder thereof when. the heatingstream has been cooled in the rectification column in this process toits dew-point, and wherein the remainder of this stream is then passedin heat exchange relationship to' the iiuidswithin the column to a pointadjacent the entry of the feed inlet and is then recycled to the. mainfeed for ultimate rectification.

It is yet. another object of this invention to provide process andapparatus. for reversibly rectifying a gaseous mixtureY wherein all theheating and cooling requirements are substantially effected by the feedand product streams both within the rectihcation column and on the feedgas itself prior to introduction in the column.

A further object of this invention is to provide process and apparatusin aV rectification column for supplying a heating fluid to the columnbeneath they feed entry to adjacent the feed entry and providing a heatexchange surface therefor which also functions as the mass transfermeans within the column. Also, means are provided for separating aportion of the heating fluid prior to passing through the entire heatexchange means together with means for varying this point of separationbetween the` top and bottom of the heat, exchange means.

it is yet. another object of this invention to provide process andapparatus for reversibly rectifying a gaseous mixture wherein theheating requirements. within the column are supplied by a portion of thefeed itself and in which part of this portion is removed from the columnprior to full heating, and all of thisv heating stream is recycled withthe main portionof the feed to the column, and the cooling requirementson the feed are supplied by the separated overhead product. which isfurther cooled by an. isentropic expansion and, after so cooling, isused to abstract. heat in continuous heat exchange relationship from thevapors of the' feed. countercurrently downto the point adjacent the feedentry to the column.

Still another object of. this invention is to provide process and4apparatus for reversibly rectifying a gaseous mixture' wherein a portionof the feed is utilized for the heating requirements within. therectification column, and this heating. is effected to a controlleddegree by cornpression of the main feed gas,V and wherein the work forthis compression is at. least partly supplied by an isentropic expansionof the most volatile separated gas from the rectification column.

Yet another object of this invention is to provide process and apparatusfor separating methane from natural gas by means of a reversiblerectification system under pressure in which the feed gas is initiallycompressedand thereby somewhat heated by work performed in an.isentropic expansion of the methane separated in the rectificationprocess, and in which the heating requirements within the rectificationcolumn are supplied by a portion of the so compressed gas. v

Other objects of this invention will appear in the detailed disclosuretaken in conjunction with the drawing illustrating a typical embodimentof this invention. It is to be understood that this drawing illustratesa preferred embodiment of this invention, is for the purpose ofdescription only, and is not intended to be limiting in e. Sclphedrawing is a schematic flow sheet showing the arrangement of the variousheat exchangers, turboexpanders, the reversible rectification column,and the flow of materials therethrough, according to the teachings ofthis invention.

Reference will be had to the drawing for showing an example of theseparation of methane from a natural gas mixture having the followinganalysis:

Per cent Methane 93.79

Ethane Propane 0.45

Butane and heavier components This mixture at 450 p. s. i. a. has adew-point of 60 F. with complete saturation at -131 F. In following theflow of materials through the process, there will be described the flowfor 100 mols of the above composition.

Briefly, the feed is first of all compressed by a blower 50 andauxiliary turbine driver 51 connected to the turboexpander 52, afterwhich it is divided up and passed to a plurality of heat exchangers andheating means in a column, then combined and introduced into thereversible rectifier for separation of methane from the heaviercomponents.

The turboexpander used in this invention may be of the conventionalradial flow type described by Swearingen in Transactions of AmericanInstitute of Chemical Engineers, volume 43, page 85, 1947, such as thatmanufactured by the Elliott Company of Jeannette, Pennsylvania.Likewise, the heat exchangers indicated at 11, 13, 14, 17, 18, 19, 20,21, 60 and 61 may be of any conventional type, such as the tube andsheet forni of heat exchanger, radial ns, etc.

Similarly, the reversible rectification column may be a packed column.The invention is, however, of particular advantage in a column in whichheat from the heating fiuid can be transferred to the mass transfersurface area, or a column in which special heat exchangers having alarge surface area are used as the mass transfer means. Such heatexchangers may be Thermek tubing heat exchangers made by Thermek Companyof Chicago, Illinois, the perforated or serrated sandwich type of heatexchanger made by the Trane Company of La Crosse, Wisconsin, or thealuminum brazed multipass extruded biscuit type of exchanger made byStacey-Dresser Company of Cincinnati, Ohio. Conventional tube heatexchangers may be equally well employed. In such heat exchangers, thesurface area for heat transfer is at least equal to that required forthe mass transfer of the liquid and vapor, so that equilibrium may beeffected continuously throughout this column in the reversiblerectification process.

It is a feature of this invention .that the surface of the heatexchangers transferring heat or abstracting heat from the iiuid beingrectified in the column acts as a mass transfer means, per se. Thisrepresents a unity of operation that effects great economies in plantinstallation as well as operating expense.

Thus, the perforated sandwich type of heat exchanger, the Thermek tubingexchanger, and the biscuit exchanger have extensive surface areas whichmay be used in the rectification column both as the heat exchange meansand the mass transfer means.

The column itself, which is generally indicated at 10, is provided withan upper heat exchanger 11 which extends from near the top of the columnto adjacent the feed entry point indicated at 12. The bottom heatexchanger comprises two sections 13 and 14 separated by a valve 15communicating with conduit 16 leading exteriorly of the column.Auxiliary valves 54 and 55, connected to conduit 16 by conduits 57 and58 and to heat exchanger sections and 61, are provided to vary theeffective relative lengths of heat exchangers 13 and 14. When any one ofthese valves is opened to conduit 16 the others are closed. Thisprovides for the dividing out of a portion of the heating fluid which isintroduced at the bottom of section 13 and then run upwardlycountercurrently to cold downcoming fluid in the column. The remainderof the heating fiuid or stream after passing through valve 15 thenpasses into section 14 and is removed therefrom adjacent the feed inletpoint 12. v

All of the heat exchangers 11, 13 and 14 within the rectification column10 are of conventional type and may be of any available form, the mainobject being, of course, the efficient transfer of heat therethroughbetween the fiuid within these heat exchange sections and the fluidmaterial exteriorly thereof in the column which is undergoingseparation.

The feed gas mixture having the above-identified composition isintroduced into the process through conduit 22. For the purpose of thisdescription the pressure of this feed gas is given as 220 p. s. i. a.and F., but this is for the purpose of description only, and it is to beunderstood that both the temperature and the pressure are subject toconsiderable variation. This pressure, however, is one that is of aconvenient value from transmission lines and is, of course, notlimiting. Conduit 22 leads into the blower portion of the turboexpander,is compressed to 450 p .s. i. a., leaves the blower at this pressure andat a somewhat elevated temperature through conduit 23 where it is cooledby water-cooled intercooler 59 to 100 F. This amount of cooling isvariable depending upon process requirements. Stream 23 is then split upinto two additional conduits 24 and 25. Conduit 24 leads to heatexchanger 17, and the conduit 2S is connected to the bottom of heat fexchanger 13 within the rectification column 10.

The feed from conduit 23 which comprises the 100 mols, for the purposeof description of this invention, is spiit into two streams, 81.9 molsgoing through conduit 24, and 18.1 mols going through conduit 25. Thisdivision is subject to the process requirements, as will be laterdescribed, which will be dependent upon the make-up of the feed gasmixture. The 81.9 mols of feed gas passing through heat exchanger 17 arecooled to -55 F. and leave the exchanger through conduit 26 whichcommunicates with proportioning valve 27. Connected to one of theoutlets of this valve is a conduit 28 which is connected to the inletside of heat exchanger 18. Through this conduit 28 is passed 39.39 molsof feed gas mixture at -55 F.

The proportioning valve 27 has another inlet connected to the conduit 16which is in communication with valve 15 at its other end. This conduitreceives 7.49 mols of feed gas which have been cooled to 55 F. in heatexchanger 13 within the rectification column, as will be more fullydescribed below. This makes a total charge of 89.39 mols of feed gas at55 F. to the proportioning valve. The proportioning valve further hasanother outlet connected to conduit 30 which communicates at its otherend with heat exchanger 21 and through which 50 mols of the gas mixtureare passed. In heat exchanger 21 this portion is cooled to F. and is ledfrom the exchanger 21 through conduit 31.

The 39.39 mols of gas leaving proportioning valve 27 and passing throughheat exchanger 18 are cooled to 10.5 F, This is combined with stream 31to make 2,713,7&1

S 89.39 mols invall cooledto l0-5 F. This combined stream is introducedinto heat exchanger 19 by conduit. 33 wherein it is cooled to 110 F. andleaves through conduit 34. l

The 18.1 mol stream of feed gas which was sentv through conduit 25 andheat exchanger 13 and from.y which 7.49 mols were removed through valve15 and conduit.- 16 now totals 10.61 mols. This stream is sent throughheat exchanger 14- whereinit is cooled tot 102 F. This stream leaves theexchanger 14 by conduit 35 andl is introduced into heat exchanger 20wherein itis cooled to 110' F. This feed gas stream comprising 10.61mols inexchanger 20 passes therefrom by conduit 36.

The two streams of feed gas in conduits 36 and, 34 comprising 10.61 molsandl 89.39 mols, respectively, are combined in conduit 37 and areintroduced into the column at entry point 12, making up` 100 mols in allat 110 F. and 450 p. s. i. a., representing a. partially saturated gas.

Returning to the first portion of the process wherein 1.8.1 mols of the.feed gas mixture are separated from` the stream 23 by conduit 25 andintroduced into the bottom of heat exchanger 13, it will. be seen thatthis entire stream is cooled toV 55.5 F. which is approximately thedewpoint of 60 F. of the feed gas mixture. The 7 .49 mols of thismixture are removed through valve. 15V and conduit 16 to be recycled tothe process since it is desired that a major portion of the gas supplyin this heating stream be reduced to as low atemperature as possible.The available cooling within the. column should not be entirely used inlatent heat of condensationA alone, which would have been substantiallythe case if this whole stream had been passed directly into heatexchanger 14 without any division. By separating out the 7.49 mols thereis left 10.61 mols which are available to be cooled to the lowtemperature of 102 F. representing the most eicient utilization of thecooling eiect within the column that is available.

The 10.61 mols passing through. heat, exchanger 14 pass out of thecolumn 10 adjacent to the iluid entry point 12 which is at 110 F. Thisportion of the feed. then passes, as previously mentioned, throughconduit 35 where it is additionally cooled in heat exchanger to 110 F.,and then directly introduced with the remainder of the feed to thecolumn.

In the rectifying column 95.91 mols of overhead product are separated at111 F.. through. conduit 53.. This overhead product which issubstantially pure methanev analyzes as follows:

This overhead product which will be. termed. methane is used forsupplying the cooling in the entire process, including all of the heatexchangers 1.7, 18,A 19, 20 and 21, and is introduced lrst into, heatexchanger 20 for that purpose. The methane stream, which in the coolingIprocess in heat exchanger 20 is heated to 109 F., is further utilizedfor cooling in heat exchanger 21 where it is in its cooling processheated up to 63 F.

This methane stream, which wasv passed from heat exchanger 20 to 21 byconduit 38, leaves. heat exchanger 21 via conduit39 at 450 p. s. i. a.which is the same pressure maintained within the column 10 and in allofthe streams previously described. The methane is then further utilizedin this process for cooling by subjecting it to an isentropic expansionwithin the turboexpander 52 wherein its pressure is reduced to 220 p. s.i. a. and a temperature of 122 F.

In the course of this, isentropic expansion work is performed and isutilized in the blower 50l which initially compresses the feed stream.Additional compression may be had where required by the auxiliaryturbine driver 51 which, can be conventionally driven by steam orgasoline. Should the feedy be introduced to the blower at higherpressures this auxiliary turbine driver may be eliminated and, ofcourse, only suchwork should be furnished by the auxiliary turbinedriver as is not available in the turboexpander which dependsl upon theprocess requirements.

The methane which has been cooled to 122 F. and reduced to a pressure of220 p. s. i. a. leaves the turboexpander by conduit 40 and is introducedat the top of heat exchanger 11 in the rectification column. Here themethane product is used to abstract heat continuously from adjacent thetop of the column where the overhead products leave, down to the pointof entry of the feed gas mixture at 12. In so doing this stream isheated a small degree to F. It is par'- ticularly to be noted that inthis reversible rectification process the refrigeration requirementabove the feed entry in the column is very small, which represents avery advantageous feature in this process as compared to conventionaladiabatic processes.

The methane stream leaving heat exchanger 11 by conduit 41 is thenfurther utilized for cooling by introducing it to heat exchanger 19. Inthe course of this cooling operation the stream of methane is heated to108 F. Subsequently, the stream is further utilized by leading itthrough conduit 42 to heat exchanger 18 for cooling purposes, in thecourse of which it is heated to 65 F.

In the last cooling operation the methane stream leaves heat exchanger18 by conduit 43 and is introduced into heat exchanger 17 and is thereinheated to 90 F. It is then recovered as an overhead product throughconduit 44. This overhead product is at 220 p. s. i. a.,v the samepressure as the metal feed gas,y and includes 95.91 mols of 97.78%methane, as above identified.

At the bottom of the rectification columnV 10 the liquid product isrecovered through conduit 45 and includes 4.09 mols of product at 450 p.s. i. a. This product analyzes as follows:

Mols

Ethane 2.70 Propane 0194 Butane and heavier products 0.45

This process makes possible very economic recovery of gases by areversible rectication process with a minimum of cooling required asdistinct from the conventional adiabatic type of rectiiication. In theconventional adiabatic rectication, heat is added in either one orseveral separate places by reboilers or the Iike, and all? the heatadded must be matched by heat abstraction above the point of the entryof the feed to the unit'. In this reversible rectification process heredescribed, the heat supplied beneath the entry point is continuouslyadded to the downcoming liquid up to the point of the feed entry', andthe heat abstracted from the vapors thereabove is only a small fractionof the heat supplied to the column.

Thus, in the example, about 26,500 B. t. u. are supplied in heatexchanger 13 and about 8,500 B. t. u. in heat exchanger 14, making35,000 B. t. u. in all. How'- ever, the heat abstracted above the feedentry point 12 in heat exchanger 11 is only 1,000 B. t. u., whereas inthe adiabatic type of rectilication 35,000' B. t. u. would have beenrequired, which is an obvious advantage of this invention both inequipment required and thel energy requirements'.

This process has been particularly described for the reversiblerectification of the gas having the above-identitied composition', butthe process is adaptable to handle richer gases, i. e., gaseous mixtureswhich have a higher percentage of ethane and heavier organicconstituents. Thus, for such richer gases a higher percentage of thefeed mixture is put through stream 24 than that described? above. Thiswill be somewhat more than the 81.9 mols in the example. For such richergases where the methane content is reduced from that described in theexample, the heating requirement beneath the entry point 12 of the feedgas mixture is less since there is less dissolved methane in thedowncoming liquid. For this reason the portion of the feed cycledthrough conduit 25 can be reduced below the 18.1 mols of the example.

In every case, however, the portion of the feed that is cycled throughconduit 25 into the heat exchangers 13 and 14 is partially divided atvalve 15 when the feed has been cooled to approximately the dew-point ofthe mixture. At this point a portion of the feed cycled through heatexchanger 13 is divided out in order that the most eliicient utilizationof the cooling effect within the rectification column be utilized. Thus,this cooling effect is not lost entirely, as far as low temperaturecooling of the feed is concerned, in latent heat of condensation incooling the heating uid. By acting only against a portion of thisdivided stream in heat exchanger 14, a much lower temperature reductionis made possible than if the entire portion of the feed cycled throughthe exchanger 13 were to be employed continuously into heat exchanger14.

Where the feed gas mixture is leaner and the methane content is higher,the reverse of the practice mentioned in the preceding paragraph withrespect to the division of the feed in conduits 24 and 25 employed.Thus, where the methane content is higher and the feed is therebyleaner, a greater portion than the 18.1 mols mentioned in the example iscycled through heat exchanger 13 and 14 via conduit 25 than mentioned inthe example. This provides for a greater heating below the feed entrypoint in the column, and thereby ensures the boiling off ofsubstantially all of the methane as a high purity overhead product.Likewise, where the feed is leaner, the feed mixture introduced to thecolumn at entry point 12 is cooled to a lower degree than 110 F.,whereas in a richer feed with less methane the feed gas mixture can beintroduced to inlet point 12 at a somewhat higher temperature than 110F.

In the case of the leaner gas with more methane, since there is agreater proportion of the feed cycled into conduit 25 through heatexchangers 13 and 14, and since there is a greater amount of overheadproduct from the top of the rectification column, more refrigerant isavailable for cooling the feed gas mixture within the process.Similarly, where the feed is richer, less refrigerating effect isavailable from conduit 25 supplying a portion of the feed to heatexchangers 13 and 14, and less overhead product in the form of methaneis available from the top of the column. Further, not as muchrefrigeration is required due to the somewhat higher temr perature ofthe feed introduced at inlet point 12.

This process is well adapted to be used on feed gases of varyingcomposition, as described above, and additional heat can be supplied atthe bottom of the rectifcation column by a conventional steam reboiler,if so desired, although the heating requirements are adapted to befurnished by the feed gas itself in compressing the feed gas mixture inthe blower of the turboexpander. Also, additional refrigeration can besupplied from outside sources, if desired, at the top of the column byconventional condensers, as will be well understood by those skilled inthis art.

As another example of the adaptability of this process, the feed gaswhich is introduced to the blower by conduit 22 and leaves at conduit 23at a pressure of 450 p. s. i. a. can be partially intercooled by aconventional intercooler by dividing the product into tWo streams withthecooled stream ultimately going to conduit 24 and the subsequent heatexchangers, whereas the uncooled portion which is heated up in thecompression stage is utilized in conduit 25 for heating purposes withinheat exchangers 13 and 14 at the bottom of the reversible rectificationcolumn. Various other modifications and alternative cycling proceduresmay be employed in this process, as will be readily apparent to thoseskilled in the 8 art, and it is to be understood that such changes andmodifications are within the teachings of this invention as heretoforedescribed.

What is claimed is:

1. A process for separating a mixture of fluids having different boilingpoints, in a vertical column type system having a uid inlet opening intothe column above the bottom thereof and a stripping section extendingdownwardly from adjacent the inlet to the lower part of the column,comprising the steps of: delivering into the column, by means of theinlet, the uid to be separated into a lower boiling point gaseouscomponent and a higher boiling point liquid component; introducing intothe bottom portion of the stripping section a fluid heat exchange mediumin indirect heat exchange relation with and at a slight temperatureabove the temperature of the material in the bottom of the column, saidheat exchange medium having an available heat content driving forcesuliicient to deliver heat to the column and vaporize substantially allof the lower boiling point component, providing thereby a rising vaporstream of the lower boiling component and descending liquid stream ofthe higher boiling point component; causing the heat exchange medium torise within the column and cooling the heat exchange medium by heatexchange with the vapor and liquid components within the column,reducing the available heat content of the heat exchange medium bywithdrawing in at least one stage a portion of the heat exchange medium,causing the remainder of the heat exchange medium to rise in the columnto impart heat to the materials in the column and cause said heatexchange medium to be cooled thereby, in a varying temperature gradientheightwise above said withdrawal point up to adjacent the inlet andmaintaining the vapor and liquid components in substantial temperatureequilibrium with another at any section in the column where said heatexchange medium is present, and withdrawing said heat exchange mediumadjacent the inlet.

2. A process for separating a mixture of fluids having different boilingpoints, in a vertical column type system having a fluid inlet openinginto the column above the bottom thereof and a stripping sectionextending downwardly from adjacent the inlet to the lower part of thecolumn, comprising the steps of: delivering into the column, by means ofthe inlet, the fluid to be separated into a lower boiling point gaseouscomponent and a higher boiling point liquid component; introducing intothe bottom portion of the stripping section a fluid heat exchangemedium. in indirect heat exchange relation with and at a slighttemperature above the temperature of the material in the bottom of thecolumn, said heat exchange medium having lan available heat contentdriving force suliicient to deliver heat to the column and vaporizesubstantially all of the lower boiling point component, providingthereby a rising vapor stream of the lower boiling component anddescending liquid stream of the higher boiling point component; causingthe heat exchange medium to rise Within the column and cooling the heatexchange medium by heat exchange with the vapor and liquid componentswithin the column, reducing the available heat content of the heatexchange medium by withdrawing in at least one stage a portion of theheat exchange medium, causing the remainder of the heat exchange mediumto rise in the column to impart heat to the materials in the column andcause said heat exchange medium to be cooled thereby, in a varyingtemperature gradient heightwise above said withdrawal point up toadjacent the inlet and maintaining the vapor and liquid components insubstantial temperature equilibrium with one another at any section inthe column where said heat exchange medium is present, and withdrawingsaid heat exchange medium adjacent the inlet, said step of withdrawingheat exchange medium including reducing the available heat content ofthe heat exchange medium to reduce and regulate the. temperatureditlerence between the heat exchange medium and the materials in the.column.

3. A process for separating a mixture of nids having diderent boilingpoints, in a vertical column type system having a iluid inlet openinginto the column above the bottom thereof and a stripping sectionextending downwardly from adjacent the inlet to the lower part of thecolumn, comprising the steps of: delivering into the column, by means ofthe inlet, the fluid to be separated into a lower boiling point gaseouscomponent and a higher boiling point liquid component; introducing intothe bottom portion of the stripping section a iiuid heat exchange mediumin indirect heat exchange relation with and at a slight temperatureabove the temperature of the material in the bottom of the column, saidheat exchange medium having an available heat content driving forcesuficient to deliver heat to the column and vaporize substantially allof the lower boiling point component, providing thereby a rising vaporstream of the lower boiling component and descending liquid stream ofthe higher boiling point component; causing the heat exchange medium torise within the column and cooling the heat exchange medium by heatexchange with the vapor and liquid components within the coltunn,reducing the available heat content of the heat exchange medium bywithdrawing in at least one stage a portion of the heat exchange medium,causing the remainder of the heat exchange medium to rise in the columnto impart heat to the materials in the column and cause said heatexchange medium to be cooled thereby, in a varying temperature gradientheightwise above said withdrawal point up to adjacent the inlet andmaintaining the vapor and liquid components in substantial temperatureequilibrium with one another at any section in the column where saidheat exchange medium is present, and withdrawing said heat exchange`medium adjacent the inlet, said heat exchange medium being added to thecolumn in the form of a gas and the portion which is withdrawn beingapproximately at a temperature at which condensation has started tooccur, and at a position within the column where the cooling. by thematerial in the column has just begun to cause condensation within theheat exchange medium.

4. A process for separating a mixture of iiuids having dierent boilingpoints in a Vertical column type system having a fluid inlet openinginto the column above the bottom thereof and a stripping sectionextending downwardiy from adjacent the inlet to the lower part of thecolumn, comprising the steps of: delivering into the column, by means ofthe inlet, the fluid to be separated into a lower boiling point gaseouscomponent and a higher boiling point liquid component; introducing, intothe bottom portion of the stripping section a uid heatexchange medium inindirect heat exchange relation with and at a slight temperature abovethe temperature of the material in the bottom of the column, said heatexchange medium having an available heat content driving forcesufi-icient to deliver heat to the column and vaporize substantially allof the lower boiling point component, providing thereby a rising vaporstream of the lower boiling component and descending liquid stream ofthe higher boiling point component; causing the heat exchange medium torise within thel column and cooling the heat exchange medium by heatexchange with the vapor and liquid components within the column,reducing the available heat content of the heat exchangemedium` bywithdrawing in at least one stage a portion of the heat exchange medium,causing the remainder of the heat exchange medium to rise in the columnto impart heat to the materials in the column and cause said heatexchange medium to be cooled thereby, in a varying temperature gradientheightwise above said withdrawal point up to adjacent the inlet andmaintaining the vapor and liquid components in substantial temperatureequilibrium with one another at any section in the column where saidheat exchange medium is present, and withdrawing' said heat exchangemedium adjacent the inlet, said heat exchange medium being added to thecolumn in the form of a gas and the portion which is withdrawn beingapproximately at a temperature at which condensation has started tooccur, and at a position within the column where the cooling by thematerial in the column has just begun to cause condensation within theheat exchange medium, said heat exchange medium being withdrawn fromadjacent the inlet at approximately the temperature of the cooled feedfluid and comprising at least part of the feed iuid prior to its coolingfor the column, so that its dew point is related in known manner to thedew point at the inlet and wherein the heat exchange medium after beingwithdrawn from the column is introduced into the inlet of the column forrectification.

5,. A process for separating a mixture of uids having different boilingponts, in a vertical column type system having a fluid inlet openinginto the column above the bottom thereof and a stripping sectionextending downwardly from adjacent the inlet to the lower part of thecolumn, comprising the steps of: delivering into the column, by means ofthe inlet, the fluid to be separated into a lower boiling point gaseouscomponent and a higher boiling point liquid component; introducing intothe bottom portion of the stripping section a iluid heat exchange mediumin indirect heat exchange relation with and at a slight temperatureabove the temperature of the material in the bottom of the column, saidheat exchange medium having an available heat content driving forcesuiiicient to deliver heat to the column-and vaporize substantially allof the lower boiling point component, providing thereby a rising vaporstream of the lower boiling component and descending liquid stream or'the higher boiling point component; causing the heat exchange medium torise within the column and cooling the heat exchange medium by heatexchange with the vapor and liquid components within the column,reducing the available heat content of the heat exchange medium bywithdrawing in at least one stage. a portion of the heat exchangemedium, causing the remainder of the heat exchange medium to rise in theco1- umn to impart heat to the materials in the column and cause saidheat exchange medium to be cooled thereby, in a varying temperaturegradient heightwise above said withdrawal point up to adjacent the inletand maintaining the vapor and liquid components in substantialtemperature equilibrium with one another at any section in the columnwhere said heat exchange medium is present, and withdrawing said heatexchange medium adjacent the inlet, said feed iiuid being cooled to atleast its dew point but above complete condensation whereby the heatexchange medium is likewise maintained above complete condensationwithin the column in order that it can provide a varying temperaturegradient at diiierent height levels and be cooled itself to decreasingtemperatures within the column at different height levels therein.

6. A processV for separating a mixture of uids having diierent boilingpoints, in a vertical column type system having a recti'iication sectionwith a fluid inlet opening into the column beneath the bottom thereofand a stripping sectionl extending downwardly from adjacent the inlet tothe lower part of the column, comprising the steps of: delivering intothe column, by means of the inlet, the fluid to be separated into alower boiling point gaseous component and a higher boiling point liquidcomponent; introducing into the bottom portion of the stripping sectiona fluid heat exchange medium in indirect heat exchange with and at atemperature slightly above the material inthe bottom of the column, saidheat exchange medium having an available heat content driving forcesufficient to deliver heat to the column and vaporize substantially allof the lower boiling point component pro viding thereby a rising vaporstream of the lower boiling component and a descending liquid stream ofthe higher boiling point component; causing the heat exchange rnedium torise within the column, and cooling the heat exchange medium by heatexchange with the vapor and liquid components within the column andwithdrawing in at least one stage a portion of the heat exchange medium;causing the remainder of the heat exchange medium to rise in the columnto impart heat to the materials in the column and cause said heatexchange medium to be cooled thereby, in a varying temperature gradientheightwise above said withdrawal point up to adjacent the inlet underconditions such that at any section in the column where said heatexchange medium is present vapor and liquid components are insubstantial temperature equilibrium with one another, and withdrawingsaid heat exchange medium adjacent the inlet at approximately thetemperature of the incoming mixture of fluids; introducing to the columna second heat exchange medium having an available refrigeration contentdriving force sutcient to abstract heat from the column and condensesubstantially all of the higher boiling point component, said secondheat exchange medium being introduced into the top portion of therectification section at a temperature slightly below the lower boilingpoint component therein, providing thereby a descending reflux liquidwhich becomes progressively richer in the higher boiling point componentas it descends the column and a rising vapor stream which becomesprogressively richer in the lower boiling point component as it ascendsthe column; causing the second heat exchange medium to descend withinthe column and abstracting heat therefrom by heat exchange with thevapor and liquid components under conditions such that at any section inthe column where said heat exchange medium is present, said second heatexchange medium vapor and liquid components are in substantialtemperature equilibrium with one another, and withdrawing said heatexchange medium adjacent the inlet at approximately the temperature ofthe incoming mixture of fluids.

7. A process for separating a mixture of fluids having ditferent boilingpoints, in a vertical column type system having a rectification sectionwith a fluid inlet opening into the column beneath the bottom thereofand a stripping section extending downwardly from adjacent the inlet tothe lower part of the column, comprising the steps of: delivering intothe column, by means of the inlet, the tluid to be separated into alower boiling point gaseous component and a higher boiling point liquidcomponent; introducing into the bottom portion of the stripping sectiona fluid heat exchange medium in indirect heat exchange with and at atemperature slightly above the material in the bottom of the column,said heat exchange medium having an available heat content driving forcesufficient to deliver heat to the column and vaporize substantially allof the lower boiling point component providing thereby a rising vaporstream of the lower boiling component and a descending liquid stream ofthe higher boiling point component; causing the heat exchange medium torise within the column, and cooling the heat exchange medium by heatexchange with the vapor and liquid components within the column andwithdrawing in at least one stage a portion of the heat exchange medium;causing the remainder of the heat exchange medium to rise in the columnto impart heat to the materials in the column and cause said heatexchange medium to be cooled thereby, in a varying temperature gradientheightwise above said withdrawal point up to adjacent the inlet underconditions lsuch that at any section in the column where said heatexchange medium is present, vapor and liquid components are insubstantial temperature equilibrium with one another, and withdrawingsaid heat exchange medium adjacent the inlet at approximately thetemperature of the incoming mixture of Iluids; introducing to the columna second heat exchange medium having an available refrigeration contentdriving force sufficient to abstract heat from the column and condensesubstantially all of the higher boiling point component, said secondheat exchange medium being introduced into the top portion of therectification section at a temperature slightly below the lower boilingpoint component therein, providing thereby a descending reflux liquidwhich becomes progressively richer in the higher boiling point componentas it descends the column and a rising vapor stream which becomesprogressively richer in the lower boiling point component as it ascendsthe column; causing the second heat exchange medium to descend withinthe column and abstracting heat therefrom by heat exchange with thevapor and liquid components under conditions such that at any section inthe column where said heat exchange medium is present, said second heatexchange medium vapor and liquid components are in substantialtemperature equilibrium with one another, and withdrawing said heatexchange medium adjacent the inlet at approximately the temperature ofthe incoming mixture of fluids, said lower boiling point gaseouscornponent being separated from the column and reduced in temperature byan isentropic expansion and subsequently used as said second heatexchange medium, and the work performed by the isentropic expansionbeing utilized in compressing one of the fluids in the process.

8. A process for reducing the cooling and refrigeration requirements inthe separation under elevated pressure and reduced temperature of amixture of fluids having different boiling points, in a vertical columntype system having a rectication section with a fluid inlet opening intothe column beneath the bottom thereof and a stripping section extendingdownwardly from adjacent the inlet to the lower part of the column,which comprises the steps of: taking the feed uid mixture at an elevatedpressure and ambient temperature and cooling the same to a reducedtemperature and delivering into the column by means of the inlet, theuid to be separated into a lower boiling point gaseous component and ahigher boiling point liquid component; introducing into the bottomportion of the stripping section a iluid heat exchange medium inindirect heat exchange relation with and at a temperature slightly abovethe material in the bottom of the column, said heat exchange mediumconsisting at least in part of said feed lluid prior to its deliveranceto the column, said medium having an available heat content drivingforce sufficient to deliver heat to the column and vaporizesubstantially all of the lower boiling point component providing therebya rising vapor stream of the lower boiling component and a descendingliquid stream of the higher boiling point component; causing the heatexchange medium to rise within the column and cooling the heat exchangemedium by heat exchange with the vapor and liquid components within thecolumn and withdrawing in at least one stage a portion of the heatexchange medium; causing the remainder of the heat exchange medium torise in the column to impart heat to the materials in the column andcause said heat exchange medium to be cooled thereby, in a varyingtemperature gradient heightwise above said withdrawal point up toadjacent the inlet under conditions such that at any section in thecolumn where said heat exchange medium is present, said heat exchangemedium, vapor and liquid components are in substantial temperatureequilibrium with one another, and withdrawing said heat exchange mediumadjacent the inlet at approximately the temperature of the incomingmixture of fluids.

9. A process for reducing the cooling and refrigeration requirements inthe separation under elevated pressure and reduced temperature of amixture of lluids having different boiling points, in a vertical columntype system having a rectification section with a lluid inlet openinginto the column beneath the bottom thereof and a stripping sectionextending downwardly from adjacent the inlet to the lower part of thecolumn, which comprises the steps of: taking the feed fluid mixture atan elevated pressure and ambient temperature and cooling the same to areduced temperature and delivering into the column by means of theinlet, the luid to be separated into a lower boiling poi it gaseouscomponent and a higher boiling point liquid component; introducing intothe bottom portion of the stripping section a fluid heat exchange mediumin indirect heat exchange relation with and at a temperature slightlyabove the material in the bottom of the column, said heat exchangemedium consisting at least in part of said feed fluid prior to itsdeliverance to the column, said medium having an available heat contentdriving force sufficient to deliver heat to the column and vaporizesubstantially all of the lower boiling point component providing therebya rising vapor stream of the higher boiling component and a descendingliquid stream of the higher boiling point component; causing the heatexchange medium to rise within the column and cooling the heat exchangemedium by heat exchange with the vapor and liquid components within thecolumn and withdrawing in at least one stage a portion of the heatexchange medium; causing the remainder of the heat exchange medium torise in the column to impart heat to the materials in the column andcause said heat exchange medium to be cooled thereby in a varyingtemperature gradient heightwise above said withdrawal point up toadjacent the inlet under conditions such that at any section in thecolumn where said heatexchange medium is present, said medium, vapor andliquid components are all in substantial temperature equilibrium withone another, and withdrawing said heat exchange medium adjacent theinlet at approximately the temperature of the incoming mixture offluids; introducing to the column a second heat exchange medium havingan available refrigeration content driving force suticient to abstractheat from the column and condense substantially all of the higherboiling point component, said second heat exchange medium beingintroduced into the top portion of the rectification section at atemperature slightly below the lower boiling point component therein,providing, thereby a descending reliux liquid which becomesprogressively richer in the higher boiling point component as itdescends the column and a rising vapor stream which becomesprogressively richer in the lower boiling point component as its ascendsthe column; causing the second heat exchange medium to descend withinthe column and abstracting heat therefrom by heat exchange with thevapor and liquid components under conditions such that at any section inthe column where said heat exchange medium is present said second heatexchange medium, vapor and liquid components are all in substantialtemperature equilibrium with one another, and withdrawing said heatexchange medium adjacent the inlet at approximately the temperature ofthe incoming mixture of uids.

10. A process for reducing the cooling and refrigera-A tion requirementsin the separation under elevated pressure and reduced temperature of amixture of fluids having diierent boiling points, in a vertical columntype system having a rectification section with a fluid inlet openinginto the column beneath the bottom thereof and a stripping sectionextending downwardly from adjacent the inlet to the lower part of thecolumn, which comprises the steps of: taking the feed fluid mixture atan elevated pressure and ambient temperature and cooling the same to areduced temperature and delivering into the column by means of theinlet, the Huid to be separated into a lower boiling point gaseouscomponent and a higher boiling point liquid component; introducing intothe bottom portion of the stripping section a fluid heat exchange mediumin indirect heat exchange relation with and at a temperature slightlyabove the material in the bottom of the column, said heat exchangemedium consisting at least in part of said feed iluid prior to itsdeliverance to the column, said medium having an available heat contentdriving force sucient to deliver heat to the column and vaporizesubstantially all of the lower boiling point component, providingthereby a raising vapor stream of the higher boiling component and adescending liquid stream of the higher boiling point component; causingthe heat exchange medium to rise within the column, and cooling the heatexchange medium by heat exchange with the vapor and liquid componentswithin the column, and withdrawing in at least one stage a portion ofthe heat exchange medium; causing the remainder of the heat exchangemedium to rise in the column to impart heat to the materials in thecolumn and cause said heat exchange medium to be cooled thereby in avarying temperature gradient heightwise above said withdrawal point upto adjacent the inlet under conditions such that at any section in thecolumn where said heat exchange medium is present, said medium, vaporand liquid component are all in substantial temperature equilibrium withone another, and withdrawing said heat exchange medium adjacent theinlet at approximately the temperature of the incoming mixture ofiluids; introducing to the column a second heat exchange medium havingan available rerigeration content driving force suicient to abstractheat from the column and condense substantially all of the higherboiling point component, said second heat exchange medium beingintroduced into the top portion of the rectication section at atemperature slightly below the lower boiling point component therein,providing thereby a descending reflux liquid which becomes progressivelyricher in the higher boiling point component as it descends the columnand a rising vapor stream which becomes progressively richer in thelower boiling point component as it ascends the column; causing thesecond heat exchange medium to descend within the column and abstractingheat therefrom by heat exchange with the vapor and liquid componentsunder conditions such that at any section in the column where said heatexchange medium is present, said second heat exchange medium, vapor andliquid components are all in substantial temperature equilibrium withone another, and withdrawing said heat exchange medium adjacent theinlet at approximately the temperature of the incoming mixture ofliuids, said feed uid being cooled to at least its dew point but abovecomplete saturation and the rst named heat exchange medium being addedto the column in the form of a gas which is comprised of, at least inpart, the feed fluid prior to said cooling so that its dew point isrelated in known manner to the dew point at the inlet and the portionwhich is withdrawn is at a temperature at which condensation has juststarted to occur, and at a position within the column where the coolingby the material in the column has just begun to cause condensationwithin the heat exchange medium and wherein the heat exchange mediumafter being withdrawn from the column is introduced in unconned mannerinto the inlet of the column for rectication.

References Cited in the le of this patent UNITED STATES PATENTS Re.12,092 Hiller Mar. 3, 1903 87,144 Collins Feb. 23, 1869 2,122,238Pollitzer June 28, 1938 2,134,700 Brewster Nov. l, 1938 2,270,852Schuftan Jan. 27, 1942 2,287,137 Ross June 23, 1942 2,503,265 HaynesApr. 11, 1950 2,658,360 Miller Nov. 10, 1953 2,666,019 Winn Jan. 12,1954 2,677,945 Miller May ll, 1954 FOREIGN PATENTS 100,564 Germany Ian.11, 1899

1. A PROCESS FOR SEPARATING A MIXTURE OF FLUIDS HAVING DIFFERENT BOILINGPOINTS, IN A VERTICAL COLUMN TYPE SYSTEM HAVING A FLUID INLET OPENINGINTO THE COLUMN ABOVE THE BOTTOM THEREOF AND A STRIPPING SECTIONEXTENDING DOWNWARDLY FROM ADJACENT THE INLET TO THE LOWER PART OF THECOLUMN, COMPRISING THE STEPS OF: DELIVERING INTO THE COLUMN, BY MEANS OFTHE INLET, THE FLUID TO BE SEPARATED INTO A LOWER BOILING POINT GASEOUSCOMPONENT AND A HIGHER BOILING POINT LIQUID COMPONENT; INTRODUCING INTOTHE BOTTOM PORTION OF THE STRIPPING SECTION A FLUID HEAT EXCHANGE MEDIUMIN INDIRECT HEAT EXCHANGE RELATION WITH AND AT A SLIGHT TEMPERATUREABOVE THE TEMPERATURE OF THE MATERIAL IN THE BOTTOM OF THE COLUMN, SAIDHEAT EXCHANGE MEDIUM HAVING AN AVAILABLE HEAT CONTENT DRIVING FORCESUFFICIENT TO DELIVER HEAT TO THE COLUMN AND VAPORIZE SUBSTANTIALLY ALLOF THE LOWER BOILING POINT COMPONENT, PROVIDING THEREBY A RISING VAPORSTREAM OF THE LOWER BOILING COMPONENT AND DESCENDING LIQUID STREAM OFTHE HIGHER BOILING POINT COMPONENT; CAUSING THE HEAT EXCHANGE MEDIUM TORISE WITHIN THE COLUMN AND COOLING THE HEAT EXCHANGE MEDIUM BY HEATEXCHANGE WITH THE VAPOR AND LIQUID COMPONENTS WITHIN THE COLUMN,REDUCING THE AVAILABLE HEAT CONTENT OF THE HEAT EXCHANGE MEDIUM BYWITHDRAWING IN AT LEST ONE STAGE A PORTION OF THE HEAT EXCHANGE MEDIUM,CAUSING THE REMAINDER OF THE HEAT EXCHANGE MEDIUM TO RISE IN THE COLUMNTO IMPART HEAT TO THE MATERIALS IN THE COLUMN AND CAUSE SAID HEATEXCHANGE MEDIUM TO BE COOLED THEREBY, IN A VARYING TEMPERTURE GRADIENTHEIGHTWISE ABOVE SAID WITHDRAWAL POINT UP TO ADJACENT THE INLET ANDMAINTAINING THE VAPOR AND LIQUID COMPONENTS IN SUBSTANTIAL TEMPERATUREEQUILIBRIUM WITH ANOTHER AT ANY SECTION IN THE COLUMN WHERE SAID HEATEXCHANGE MEDIUM IS PRESENT, AND WITHDRAWING SAID HEAT EXCHANGE MEDIUMADJACENT THE INLET.